Promesostoma cubitum, Diez & Monnens & Wuyts & Brendonck & Reygel & Schmidt-Rhaesa & Artois, 2023

Diez, Yander L., Monnens, Marlies, Wuyts, Arlien, Brendonck, Luc, Reygel, Patrick, Schmidt-Rhaesa, Andreas & Artois, Tom, 2023, Taxonomy and phylogeny of Dalytyphloplanida Willems et al., 2006 (Platyhelminthes: Rhabdocoela), with the description of a new family, a new genus, and sixteen new species from Cuba and Panama, Organisms Diversity & Evolution (New York, N. Y.) 23 (4), pp. 631-681 : 656-657

Promesostoma cubitum sp. n. Artois & Diez

(Figs. 13a, b and 15c)

urn:lsid:zoobank.org:act:EF102DE1-EB7D-42A9-95F7-99C083E04918

Material and distribution. Panama: Five specimen studied alive and whole mounted, one of which is designated holotype ( ZMH, No. V13688 ) and the others paratypes (HU, No. 873–876), collected in Bahía Can Can (type locality), near to Portobelo, Atlantic side of Panama (29 February 2016) . Two specimens, including the holotype, collected subtidally in a lagoon, in fine-grained sand with some organic matter taken in between sea grass, 0.2 m deep at low tide; the other three specimens collected intertidally, in well-sorted and fine sand from channels in mangroves.

Etymology. Species named after the fact that the stylet shows an elbow-like proximal extension. Lat. Cubitum: elbow.

Diagnosis. Species of Promesostoma with eyes. Copulatory bursa present. Seminal vesicle, prostate vesicle, and male atrium with stylet located caudal to the pharynx. Slightly curved stylet~ 118 µm long, with a pointed elbow-shaped, angular projection just distally to the proximal funnel-shaped part.

Description. The overall organisation is comparable to that of other species of the genus Promesostoma (see Luther, 1943; Ax, 1951, 1952; Karling, 1967). Measured on the whole mounts, the animals are 1–1.1 mm long (n = 2), translucent, with a pair of eyes (Fig. 13a: e). Anterior adenal rhabdite tracts are present (Fig. 13a: ar). The pharynx is located at 50% (Fig. 13a: ph); it is 117–182 µm in diameter (x = 152 µm; n = 3) measured on the whole mounts.

A pair of testes (Fig. 13a: t) is located anterior to the pharynx. The seminal vesicle, the prostate vesicle, and stylet are located caudal to the pharynx. The vasa deferentia run caudal and fuse to form a single seminal vesicle (Figs. 13a and 15c: sv), which narrows distally to enter the prostate vesicle (Figs. 13a and 15c: pv) and runs axially through it. On the whole mounts it was impossible to assess whether or not the seminal vesicle is surrounded by a muscle layer. The prostate vesicle itself connects to the stylet. The male atrium receives the well-developed male copulatory bursa and the stylet. The stylet (Figs. 13a and 15c: st, 13b) is 108–123 µm long (x = 118 µm; n = 5). Proximally it is funnel shaped, 8–10 µm wide (x = 9 µm; n = 5). Caudal to the funnel, the stylet shows a pointed angular projection, which is somewhat elbow shaped. The distal end of the stylet is widened, with the distal opening of the stylet completely at the end. The male copulatory bursa (Figs. 13a and 15c: mb; terminology of Karling, 1967) is located beside the pharynx and opens into the male atrium at the level of the projection of the stylet. The paired vitellaria (Fig. 13a: vi) extend along both body sides, from the eyes to the caudally located, oval-shaped ovaries (Fig. 13a: ov).

Fig. 13 a, b Promesostoma cubitum sp. n. c–d, Promesostoma panamensis sp. n. a, c

Body organisation. b, e Stylet

(from the holotype). d Schematic reconstruction of the male genital structures. Structures oriented with the anterior end toward the top of the plate